CROSS REFERENCE TO A RELATED APPLICATION
Cross reference is made to a related patent application entitled Method of Manufacturing a Pump With a Modular Cam Profile Liner, filed on Feb. 28, 1994, given U.S. Ser. No. 08/202,360 and assigned to the assignee of the present application.
I. Field of the Invention
This invention relates generally to rotary fluid transfer devices, and in particular, to pumps having flexible impellers which can be run dry for an extended period of time.
II. Discussion of the Prior Art
Flexible (elastomeric) impeller pumps function due to an impeller or rotor rotating within a housing chamber and within close tolerances of the chamber walls. A sophisticated cam profile is usually provided within the housing chamber to effect a pumping action. The impeller passes over this cam profile, fluid is caused to be displaced from a suction port to a discharge port, each port being in fluid communication with the pumping chamber. Flexible impeller pumps have been in existence since the 1940's, and have primarily been used for marine engine cooling applications, although there are pumps of this variety used for the industrial transfer of fluids. When in operation, the pumped fluid cools the impeller, and provides for a lubricating film between the impeller and the housing chamber walls. Occasionally, these pumps are required to run dry for limited periods of time. This can be due to long suction lift, operator error, or due to accident such as the intake of the pump becoming clogged.
Under dry run conditions, the friction between the flexible (elastomeric) impeller and the housing rapidly increases. This friction generates heat which causes the impeller temperature to rise until the elastomeric impeller is damaged, or even self destructs. At this time, the impeller loses its ability to pump, and can totally fail. The heat is generated in two primary locations. First, between the impeller distal ends and the cam profile as they are swept across the profile, and secondly, between the impeller hub and the end or side walls of the pumping chamber.
U.S. Pat. No. 2,336,580 to Yeatman discloses an artery-type rotary pump. A sleeve-type rotor is journaled for rotation within a housing. The rotor has a pair of end plates forming an integral portion of the rotor, and thus, rotate therewith. A pair of chambers are provided, one each side of the rotating rotor end plates. These chambers provide lubrication via grooves between the arcuate perimeter of the rotor and the housing inner wall. The pumping action is produced by the expansion and contraction of the cavities formed between the inner and outer rotor sleeve. The rotor is not disposed between and frictionally engaging any fixed end plates, which plates define a pumping chamber.
U.S. Pat. No. 3,386,386 teaches a pump having an external container for storing and feeding liquid to a pumping chamber. Fluid is communicated to the pumping chamber through a wall defining the pumping chamber. Similarly, U.S. Pat. No. 2,636,443 to Rand teaches an external reservoir also communicating a fluid to a pumping chamber to reduce friction and wear if the pump is run dry.
U.S. Pat. No. 3,161,135 to Eriksson teaches a pump having a water pressure switch. This switch senses water pressure, and insures the pump is run only when there is adequate water pressure at the nozzle such that it is not run dry. U.S. Pat. No. 2,455,194 to Rumsey teaches a rotary flexible vane pump with a hub having recessed areas to permit the liquid pump to wet the casing and hub surfaces while rotating.
U.S. Pat. No. 2,664,050 teaches a pump for a washing machine having chambers for trapping liquid within the mechanism to provide automatic lubrication thereof. These chambers are defined in series with the inlet and outlet ports. In an alternative embodiment, the whole pump itself is encased within a second housing filled with fluid. The fluid trapped within this casing helps conduct any heat which is generated by the rotor, and dissipates the heat into the fluid to prevent any high temperature of the rotor.